Nickel base alloys



- July 19, 1960 p JAHNKE ETAL 2,945,758

NICKEL BASE ALLoYs Filed Feb. 17, 1958 5765.55 EaP/*M35 (mf/a/v f 0N We 57064/ United States Patent This invention relates to nickel base alloys. More particularly, it relates to nickel base alloys which include a critical range of aluminum and titanium topren duce unusual high strength properties at both low and high temperatures.

In order to advance the technology of operations such.

as that of high temperature operating turbines inwhich,V both low and high temperatures as well as high stresses...V

are encountered, it has been necessary to develop ma-V terials having unusual strength properties at operating,

temperatures.

Nickel base alloys have been attractive for such uses but have had, heretofore, strength liiiiita-YYY tions which have precluded their use for high stress apv plications-- especially at high temperatures.

VAttempts have been made to strengthen nickel base alloys using combinations of molybdenum, titanium and aluminum as ingredients of the alloy and still maintain reasonableworkability and ductility. Relatively broad ranges of theseelements` have been reported in nickel base alloys, but it has never before been recognized that a certain critical and narrow range of proportions of titanium and aluminum will produce certain unexpected properties. It has likewise. never been recognized that special heat treatments coupled with these ranges of proportions will enhance these properties even further.

For severall years ,air melted nickel base alloys containing about 2.5% titanium and about 1% aluminum were considered to possess the near optimum balance of high temperature strength consistent with reasonable forgeability. It was thought that. larger additions o f titanium and aluminum might increase theV strengths but would surely decrease the ease of melting in airand forgeability to a non-commercial level. The entrance of vacuum melting into this field made possible an crease in the percentages of the reactive elements, better forgeability and improved properties. Y

Consequently, it is a primary object of our invention to produce improved nickel 'base alloys having a critical range of titanium and aluminum to produce for both low and high temperatures, high strength properties heretofore unpredictable and unexpected in reported wider alloy ranges. Y

Another object is to provide a nickel' base' alloy which, when made into sheet' form, has unusual strength properties for' both high and low temperature applications for lightweight design. g

Still another object to provide a nickelbase alloy which when made into forgings, has improved strength properties especially in large discs.

An additional object is to provide heat treatment cycles which will enhance` the increased high strength properties resulting from theuse of a critical range of titanium and aluminum.

These and other objects of our invention will become apparent from the attached drawing, the detailed description and the claims whiclrfollow. jj

Briey stated, in accordance with one aspectof our invention, we provide a composition range for an 1mproved nickel base alloy for use up to about 1800 comprisingin percent by weight about 0.06-0.20 carbon, V18-20 chromium, 9-12 cobalt, 9-10.7l molybdenum, 3.0- `3 :3 titanium, 1.31.9' aluminum, up to about 0.02 boron, with the balance essentially nickel and impurities.` -In order to enhance'our greater strength properties, we prof vide-methods for heattreating our alloys to produce-high tensile strength up to elevated. temperatures comprising heating atabout. 1950 F. for aboutone-half hour, rapidly cooling tov about room temperature and then heating at about l4 0 0 F. for about 16 hoursbefore cooling. In addition we provide methods for-:heat treating our alloys to produce high stress rupture strength up toelevated temperatures comprising heating at about 2l50 F. for about one half hour, rapidly cooling to about room temperature and then heating at a temperature of about 1650D F. for about Yfour hours before cooling; s

In studying various additions of aluminum and titanium to nickel base alloys containing molybdenum, We have noticed that very small changes incomposition resulted 'Y in wide, unpredictable changes in properties'. In addition, the combination of such new alloys with,.variousheat treatments gave even higher, unexpected'strength. properties.. Althou'gll'such. high strengths..arehattractive for forgings they are especially desirable 'an'dj heretofore unavailable in sheet materials to be used. at elevated teni'- peratures, for example upto about 1800" Indeveloping heat treatments and our vcritical compositionVv range, it was necessary to prevent during cooling from 19.50- 2150 the massive and untimely formation of undesirable phases of age hardening constituents which decrease the; formability of high temperature aluminum-bearing, nickel base sheet. alloys after 4heat treatment. Our improved alloy is essentially a new product since it has properties which far exceed all reported sheet materials at elevated temperatures. Therefore its utility extends to temperatures higher than that of other knownA sheet materials.` A

Two of the tests generally performed on alloys to discover, their physical properties are stress rupture and tensile tests. The results of these tests, reported as stress rupturestrcngth and tensile strength respectively, are generally defined as follows:

Stress rupture strength is the steady stress which a specimen will sustain Without fracture for a given length of time (soften 1,00 or 1000 hours).

Tensile strengthf sometimes called ultimate strengt is. the maximum stress which Aa specimen is capable of sustaining without fracture when the stress is continuously and quite rapidly increased during the testing period.

Both stresses mentioned above are obtained by dividing the load on the specimen at the time of fracture by the original cross sectional area of the untested specimen.

Our alloy when vacuum melted has the advantage of a 40% increase in tensile strength properties and a 60% increase in stress' rupture strength over vacuum melted alloy A i'n Table I below and is 65% greater in tensile vstrength and 50% greater in stress rupture strength than vacuum melted alloy B in Table I below. iBoth alloys A and B are widely used high temperature materials. In addition, our alloy has remarkable formability and weldability properties despite the increase in titanium and aluminum over-former usable similar alloys. l

lOur alloy range and its heat treatment will be better understood from our description taken in conjunction 'with the accompanying ldrawing and the following` examples. whicli are given by way of illustration only and not in any Way by limitation. The scope of' our invention will be pointed out in the claims.Y

in. the drawings; Figure 1 is a graph the curves of which compare stress rupture strength of our alloy with other currently available elevated temperature alloys.

Figure 2 is a graph the curves of which show the scatter band` of stress rupture strength of sheet materials made from our broad alloy range. As shown in Figures 1 and 2, stress rupture strengths are represented by a comparison of stress with a timetemperature parameter shown at the horizontal coordinate. This parameter has been calculated from the formula P=T(20}log t) 103 in which P=the timetemperature parameter number, T=absolute temperature in degrees Rankine and t=the time in hours.

These curves have been prepared from a large amount of stress rupture test results and represent a compact summary of such data. The nominal composition of 4,alloys A, B, C, D and E of Figure 1 are compared in the following Table I:

a lower titanium content as well. Examples 4, 5 `and 6 include aluminum at higher percentage ranges than our critical range. This bar stock was prepared rfor stress rupture testing by a solution heat treatment of about one hour at about 2100 F. in order to attain full solutioning and still obviate grain coarsening in the lower titanium and aluminum alloys. Solution heat treatment is a process in which an alloy is heated to a suitable temperature, is held at this temperature long enough to fallow a certain constituent to enter into a solution called a solid solution and is then cooled rapidly to hold the constituent in solution. The metal is left in a supersaturated, unstable state and may subsequently exhibit age hardening. The process of age hardening is a hardening process which by holding an alloy at a given temperature for a period of time increases hardness and strength.

Table I NOMINAL PERCENT BY WEIGHT OurAlloy A B O D E 0. 1 0. 04 0. 1 19 balance balance balance 15 Cobalt 11 balance 19. 5 10 Figure 1 shows our alloy to be superior in stress -rupture strength to currently available elevated temper- -ature materials, the compositions of which are shown in Table I above, when all materials have been heat treated to give optimum stress rupture properties. The three strongest alloys of Figure l, namely our alloy and alloys C and E, were solution heat treated in the 2000-2150 F. range. Although the composition of our alloy and of alloys C and E diier essentially only in the aluminum and titanium content, our alloy after being solution heat treated in the same range as alloys C and E, shows a marked increase in strength.

Figure 2 shows the upper and lower stress rupture ranges of our alloy when made into a series of sheet materials solution heat treated at 2150 F. for one hour and subsequently age hardened at 1650 F. for 4 hours from the following composition range in percent by Weight: 0.06-0.20 carbon, 18-20 chromium, 9-12 cobalt, 910.7 molybdenum, 3.0-3.3 titanium, 1.3-1.9 aluminum, up to about 0.02 boron, up to about 0.5 silicon, up to about 0.5 manganese, up to about 5. iron with the balance essentially nickel.

EXAMPLES 1-6 In order to determine initially the eiect of aluminum on our alloy range, a series of alloys having the following compositions was vacuum melted:

The alloys of Examples 1-6 were then forgedY without difculty into 1/2 diameter bar stock. `It is to be noted that the only alloy within our novel and critical range is that of Example 3. The alloys of Examples 1 and 2 contain lower percentages of aluminum, Example 1 having All specimens were machined in this condition to proper testing configurations and subsequently age hardened at 1650 F. for about 20 hours. Aiter age hardening, the reduced sections were hand polished to remove the small amount of oxide which had formed. Table III below compares the stress rupture strength of the alloys of Examples 1-6:

Table lll hour stress rupture strength 1,000 p.s.i.) Example Alloy vAs seen in Table III, the 'alloy of Example 3 has higher stress rupture strength than any of the other alloys of Examples 1-6 thus showing a critical range and a peak of strength between 1.18% and 2.16% by weight aluminum.

In one of the tensile ductilty tests which we made and which is a measure of the permanent deformation before fracture by stress in tension, we compared one alloy including a lower percentage of aluminum and one alloy including a higher percentage of aluminum with an alloy within our novel range. The following Table IV which shows a tensile ductilty comparison at-l500 F. reports ductilty as percent elongation, the amount of permanent extension in the fracture area vin a tension test, and also as percent reduction in cross sectional area that occurred during the stress application.

' Table l V Percent Percent Example Alloy Elongation Reduction (in 1 inch) in Area 2 19 59 a 31 so .s 26 51 emerges Although we had obtained excellent results using b'ar stock made Ifrom material within our critical alloy range, We were extremely interested -in producing from our alloy a sheet material which would have superior propertres. terials-*from aluminum-bearing, nickel base alloys is. the prevention upon L'Gooling after 4'heat treatment of the massive lrformation-"of undesirable phases of age hardening constituents which decrease 'the 'formability of such sheet material.

'The following Examples 7-9 showfthe Qre'sults of our fheat treating an alloy within our --criticalcomposition l:range to overcome the .formation lof vilndes'ralilefphases in our alloy sheet. For use in Examples 7-9 analloy heat No. ?l-985 -of-the following 4compositionwithin our novel range was melted and formed into sheet material of 0.10.63" thickness:

Percent by weight Carbon 0.1 Y Aluminum 1.7

Titanium v 13:1 Molybdenum y10.5 Chromium 19.l Cobalt 9.4 Silicon "0:03

Manganese 0.03 Nickel .and impurities .Balance We used the following .heat treatment cycles:

Example 7.-ASolution'heat treat at .1950 `Fioronehalf hour, airzcool to about room temperature, ageharden at 11400" F. for sixteen hoursa'nd then aircool.

Example '8.-Solution heat treat at 21'5 0 F. vfor onehalf' hour, air cool to about room temperature, age lharden at l'1400"I F. for sixteen hours Vand then air cool.

Example 9.-Solution'heat treat at'2150' F. for onehalf hour, air cool to about room temperature, ageharden atfl6'50" for sixteen hours vkand then air cool.

Table 'V below compares stress rupture data-obtained from `sheet material heat `treated according -to Examples A problem 'existing'inthe production of sheet ma- Aseries of 'specimens were y,prepared V'from the 0.063" thick -sheet material vobtained from our alloy lheat No. 3-985 by 'heat treating -according to Examples "7 and 8. 'Thesefspecimens were then shaped into the proper form for tensile strength testing. In addition to the tensile Strength, we ydetermined the v0.2% yyield strength which is 4the stress at which a material exhibits v0.2% .permanent extension. This `tigure, sometimes called 0.2% offset, ;is commonly used as a .design :criterion Vfor strength.

The following Table VI shows the vaationof ulnensile Vstrength properties of :our alloys 7with heatv itreatmet cycles: Y

Table VI Tensile Strength u 0.2% Yield Strength 1(1,000 p.S.i.) (1,000 p.S.i.) Temperature F.') Y f Y l =1=r.i'r. n. T. H. T. H. fr. -Example 7 Example 8 Example 7 Example 8 f 191. 5 152 150 123 167 150` 135 .1108.25 I, 157 105 12?.'5 98. 5 137 115 119. 5 102. 5 1115. s 107 107. 5 Y 93 As seen from Table VI above, the heat treatment of 'Example 7 results 'in superiorgprop'erties toftlrat Jof 'Ex'- ample 8. Comparing the results :ofboth stress rupture and tensile .strength variations with vheat ttre'atments, it is noted :that .-to obtain superior stress 'rupture strength, it :is =better fto -solution heat treat :at A2-150 TF. .rather 'than Vat 195.0" F.1and to age :harden at l650 aF. .rather-than 1400 F.g and in order to obtain superior tensile fstrength, it is better to solution heat treat at l950 F. rather than at '2.150'o `P."an'd to ageh'a'r'den 'a't12l00` E 'These unusual characteristics for our alloy allow us to desig- V nate j a Ydifferent 'heatjtreatrnent 1in order ato obtain .either high lstress rupture strength or high tensile strength, whichever the designer-of an article may require.

`In .order .to compare our Yallo.)l heat .treated to its op.- timum strength with an alloy Whose composition closely resembles that of our alloy but was slightly dilerent in the titanium and 'aluminum content, we prepared sheet materials from the following two alloys:

Percent by Weight Anny f A' Y u C Ar '11 Mo yor 00 Nr-l'- :Impur'ltle's Marsa. 0.19 V`1.15. 2-51 9.7 .20.0 .9.9 .Balance J-41A 0.15 1.60 3.1l 9.4 10.1 9.4 Do.

The results of'rtensile `testing on sheet-material pre- =pared from these alloys and heat treated according .to the optimum `conditions given in .Examplef'are'show'n inthe following Table VII A Table VII l" Y.

, Tensnestrength Y Y .0.2% xiudsnnigni4 -(1,000 ps1.) (1,000 ps1.) Temp. F.) f f M-zsz J-41A Mlzz J-.41A

180 183 79 111s 157 160 .71 ,10a 152 161 70 10o l 13a 'fas k e7 70 91 36l .56

.From Table VII it is easily apparent that the -small variation in titanium and aluminum content, coupled with an optimum heat treatment gives a greatly improved tensile strength results. l Y A A test used for determining the formability of an alloy is known as the Erichsen lCup Test. IIt is a .typepf ductility test .for sheet material which measures the 'depth lin millimeters of an impression at fracture, made by forcing a cone-shaped plunger into a specimen. The greater the depth vof depression, the better is fthe lf'rniability.

The following Table V'III shows the results 'of Erichsen `Cup'testing on the alloys of this 'example whichweresolution heat treated at 1950* F. for one half Ahour'and then cooled las indicated. Although the compositions fof -M2752 and our J-41A are essentially the same except '"7 for the critical variation in aluminum and titanium content, our J-41A has a much higher degree of formability.

perior to other alloys, certain physical characteristics are improved by the inclusion of boron. To exemplify these increased properties, we melted alloys of the following compositions:

-8 An additional example of the average tensile strength ofvrour alloy is given in Table XI below. This data was accumulated from tensile tests of sheet materialsolution heat treated at 1950 F. for one half hour, air cooled to room temperature, age hardened at 1400 F. for sixteen hours and then air cooled.

In the foregoing description we have disclosed an Percent by Weight Exam 1e Heat No.

p Y A(J Cr Co Mo Ti Al B Niand Impurities 11 VA-157- .1 18.6 11 10 3.12 1.78 1.003 Balance. 12 V-5 .1 18.7 10 10 3.17 1.89 .005 Do.

' lMax.

Table IX below compares the stress rupture strengths of the alloys of Examples 11 and 12 and shows that an increase in boron increases strength. The alloys of Examples 11 and 12 were each solution heat treated at 2150 F. for about one half hour, air cooled to about room temperature, age hardened at about 1650 F. for

One way of representing the relationship of stress rupture strength to time and temperature is to use the formula P==T(20llog t) X103 as defined before. Some data from which the scatter band of Figure 2 was produced and data which is representative of our alloy range when solution heat treated at about 2150 F. for one half hour, air cooled to about room temperature, age hardened at about 1650 F. for about 4 hours and then air cooled is given in Table X:

Table X Hours to Failure Parameter Temperature Stress F.) (psi.)

Min. Avg. Max Mm. Avg. Max

improved nickel base alloy for use up to about l800 F. and methods of heat treatment for such alloy to enhance the improved strength properties depending on intended use. Although we have described our invention in connection with specific examples, these examples are to be construed as illustrative of rather than limitations on our invention. Those skilled in the art of metallurgy and heat treatment will readily understand the modifications and variations of which our invention is capable, for example, as to the limit of allowable variation of time, temperature and atmosphere in heat treatment cycles and as to the variation of the composition of our alloy within the limits of alloy melting procedures and quantitative analytical methods. We intend in the appended claims to cover modifications and variations that come within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An improved nickel vbase alloy suitable for 4use at elevated temperatures comprising in percent by Weight: 0.06-0.20 carbon; 18-20 chromium; 9-12 cobalt; 9-10.7 molybdenum; 3.0-3.3 titanium; 1.3-1.9 aluminum; with the balance essentially nickel and impurities.

2. The alloy of claim 1 which includes up to about 0.02% by Weight boron.

3. The alloy of claim 1 which includes in percent by weight: up to 0.5 silicon; up 'to 0.5 manganese; and up to 5. iron.

4. An improved nickel base alloy suitable for use at elevated temperatures comprising in vpercent by weight: 0.06-0.12 carbon; 18-20 chromium; 10-12 cobalt; 9-10.7 molybdenum; 3.0-3.3 titanium; 1.3-1.8 aluminum; up to about 0.02 boron; with the balance essentially nickel and impurities.

5. An improved nickel -base alloy suitable for use at elevated temperatures comprising in percent by Weight: 0.06-0.12 carbon; 18-20 chromium; 10-12 cobalt; 9-10.7 molybdenum; 3.0-3.3 titanium; 1.3-1.8 aluminum; 00005-0015 boron; with the balance essentially nickel and impurities. f i' 10 References Cited in the le of this patent UNITED STATES PATENTS 6. An improved nickel base alloy suitable for use at elevated temperatures comprising in percent by weight: (L08-0.15 carbon; 18.519.5 chromium; 9.4-11 cobalt;

nickel and impurities. 

1. AN IMPROVED NICKEL BASE ALLOY SUITABLE FOR USE AT ELEVATED TEMPERATURES COMPRISING IN PERCENT BY WEIGHT: 0.06-0.20 CARBON, 18-20 CHROMIUM, 9-12 COBALT, 9-10.7 MOLYBDENUM, 3.0-3.3 TITANIUM, 1.3-1.9 ALUMINUM, WITH THE BALANCE ESSENTIALLY NICKEL AND IMPURITIES. 